Stetler's letter was received Tuesday morning, said Gov. Ed Rendell's chief of staff, Steve Crawford.
Attorney General Tom Corbett planned an afternoon news conference to disclose additional arrests in the three-year investigation into the Legislature's campaign and financial practices that has already resulted in charges against 22 people.
Stetler represented a York district from 1991 to 2006 and had been a leading campaign strategist for the House Democrats from 2003 to 2006. Rendell appointed him revenue secretary last year.
Rendell disclosed nearly two weeks ago that Stetler had been asked to testify before an investigative grand jury.
The attorney general's office would not say whether Stetler is among those to be charged. Stetler's lawyer, Josh Lock, did not immediately return telephone messages left by The Associated Press on Tuesday.
The Pittsburgh Post-Gazette, Philadelphia Inquirer and Patriot-News of Harrisburg all reported earlier this month that House Majority Whip Bill DeWeese, D-Greene, also received a grand jury letter. The Post-Gazette reported that Majority Leader Todd Eachus, D-Luzerne, also received a letter. The newspapers did not reveal the sources of the information.
DeWeese's spokesman and lawyer did not return phone messages seeking comment. Eachus spokesman Brett Marcy said he had no information about what Corbett was about to announce, and neither Eachus nor his lawyer returned messages.
Corbett has previously charged 12 people associated with the House Democratic caucus and 10 people with ties to House Republicans, including Philadelphia Rep. John M. Perzel, the former House speaker.
In the only case to go to trial so far, former state Rep. Sean Ramaley of Beaver County was acquitted.